I mean no disrespect but I think you need to get absolute confirmation with your gunsmith, before, he ever sticks a reamer in your barrel because one of you seems a little confused.
The new, actual, 7 PRC IS NOT the same as a necked up 7-6.5PRC. The 6.5 PRC case is substantially shorter and no amount of fireforming will, safely, stretch a 6.5PRC case to make 7 PRC brass.
Now, if your smith is talking about building you a 7-6.5PRC well that is an entirely different cartridge then a actual 7 PRC. The 7-6.5PRC is just a necked up 6.5 PRC case to 7mm.
You really need to have a discussion with your gunsmith before you proceed with anything and find out if he's talking about building you a actual 7 PRC or a 7-6.5PRC because they are far from the same and the brass is not interchangeable.
He's a pic of how much different the length of a 6.5 PRC is to the new 7 PRC.
backfire.tv